The invention herein relates to aerosol valves and more particularly is concerned with a novel valve construction for a pressurized package in which the metering of the pressurized product remains constant for the life of the package and may be accurately established at the time of manufacture of the valve.
Aerosol valves are generally of two types, namely those in which there is a stem protruding from the package and a button is removably mounted on the stem, and those in which the stem and button are integral to provide a sprayhead that may be totally removed from the package. Somewhat different techniques are used in gassing the two types. The invention herein is applicable to both types of aerosol valves and a principal attribute of the invention, namely accurate metering, is available for both constructions. Other advantages will be described in connection with the respective types.
The so-called aerosol package of the present time is a canister or bottle of robust construction capable of sustaining relatively high internal pressures, having some material therein which is to be atomized or sprayed, this material being suspended in or mixed with a propellant. The propellant is usually gas having a low boiling point maintained under pressure. The canister or bottle is provided with an opening in its upper end and a valve assembly is mounted in this opening.
The preferred embodiments of the invention will be described herein as mounted to canisters, but it should be kept in mind that the invention is equally advantageous when the container for the pressurized product is a bottle.
Since the manufacturing techniques for canisters on the one hand and valve assemblies on the other hand are quite different, the one who assembles the packages, called a filler, purchases the valve assemblies and canisters separately and assembles them on his own production line. The opening in the canister has a rolled edge and the valve assembly includes a cover member that fits over the opening and is crimped in place. Filling of the package is accomplished with several different techniques, depending upon the nature of the product and its propellant, the type of filling equipment which the filler has, and the construction of the valve. Most economical types of filling techniques are those by means of which the package is gassed after it is completed, at room temperature directly through the valve.
The valve assembly which the filler purchases from the manufacturer comprises a metal cover member which has a downwardly opening annular partially rolled edge that engages over the rolled edge of the opening of the canister, there being some gasketing compound baked into the rolled edge of the cover member so that when crimped in place a permanent seal will be formed. The cover member has a central upwardly protruding boss surrounded by a well of annular configuration, the boss protruding almost to the same level as the rolled edge of the cover member. It has a center opening into which the stem of the sprayhead is adapted to pass. As used in this specification, the sprayhead will be considered to be composed of a button and a stem, whether integral or separate.
On its underside, the boss of the cover member has the upper end of a valve housing crimped thereinto, with a disc-like annular gasket member of elastomeric material sandwiched between the upper end of the valve housing and the lower surface of the top of the boss. There is a passageway in the elastomeric gasket aligned with the opening of the boss so that the stem of a sprayhead may be slidably and sealingly engaged therein. There is a valve plunger in the housing which is spring-biased against the gasket member, the stem of the sprayhead engaging in a socket formed in the plunger, the upper edge of the plunger serving as a valve seat to control whether or not pressurized product will pass from the interior of the package by way of a dip tube to the valve housing, over the valve seat and into the hollow bore of the stem and thence to the button of the sprayhead.
The construction described is disclosed in U.S. Pat. No. 2,777,735. In this patented construction, the stem of the sprayhead has a slot in its side wall which extends axially along the stem from the bottom end thereof to just above the valve seat so that it enters the gasket. Pressing down on the button exposes the upper end of the slot below the elastomeric gasket member so that the pressurized product enters into the bore of the stem only by way of the exposed portion of the slot. Thus, the cross section of the slot entrance controls the rate at which pressurized product is passed to the hollow bore of the stem and out the external opening of the button. This is called metering, in the art.
The so-called slotted stem sprayhead has enjoyed substantial success, especially in handling products which have heavy materials in suspension, such as for example waxes, paints and the like. One problem which arose in such valves concerned the control of metering. Two factors would alter the metering which was built into the stem of the sprayhead. One was the constricting force of the elastomeric gasket tending to close the slot and the other was the swelling of the resinous material from which the sprayhead was molded. In both cases, the tendency of the slot was to close, substantially changing the metering and often even closing the slot so that very little if any of the product could be passed. This was especially true in the case of very fine metering where the slot initially was quite small. Because of the above factors, sprayheads of this type were made out of some synthetic resin which was relatively rigid, such as nylon. Other similar resins used were those sold in the market as trade-marked products "Delrin" and "Celcon," these also being relatively rigid. The degree of cold flow of this type of synthetic resin is less than the softer resins, among which are polyethylene and polypropylene. The cost of the softer resins is substantially less than that of the rigid resins, but the latter were needed in order to maintain the metering dimensions molded into the stems. Polypropylene is a soft resin but somewhat more expensive than polyethylene although more economical than the rigid resins or plastics, as they will be referred to herein.
Two constructions were devised to obviate the problem of collapsing slots, one of which consisted of placing a small strengthening web in the upper end of the slot, and the other of which was to provide an interior gallery in the socket of the plunger so that the slot of the stem need not enter the elastomeric gasket. The first of these constructions is disclosed in U.S. Pat. No. 3,045,877 and the second of these constructions is disclosed in U.S. Pat. No. 3,233,792.
While these constructions at least partially solved the problem of relieving the section of the stem where the slot is from the constricting forces of the elastomeric gasket, the problem of swelling was still present. Additionally, molding sprayheads with metering slots is expensive because of the complexities of the molds and the need for maintenance and repair. Additionally, for every different type of metering the molds must be different. Since the part of the sprayhead which is involved is so small, the difficulties involved should be obvious.
The invention achieves advantages over the prior art, especially for cases where the metering is fine, by using a construction that provides a sprayhead in which the stem is imperforate and hence is more economical. The molds for the sprayheads are all simple to manufacture and are all the same irrespective of the metering. Additionally, instead of being molded of rigid resins, these sprayheads can be made of the softer resins of which polyethylene and polypropylene are examples. Considerable savings are achieved by using the more economical of the resins, i.e., the soft resins.
The invention is applicable to stem valves by means of a novel construction. Stem valves are disclosed in U.S. Pat. Nos. 3,266,678 and 3,348,743, although in the latter patents the stem was of complex structure utilizing metering slots molded therein. According to the invention herein, the stem is independently molded without any perforations therein and hence is capable of being made for all meterings without change. The stem valve of the invention may also use a soft resin button which gives advantages in cost.